This invention is related generally to propulsion units for boats and, more particularly, to marine jet drives.
Marine jet drives which propel vessels by means of water jets have long been known and used, and have certain significant advantages over the traditional external propeller units. A typical marine jet drive includes an engine-driven impeller which rotates inside an impeller housing. The impeller pumps water from below the vessel through a water intake duct, and then pressurizes and expels the water through a diffusor housing and a nozzle behind the vessel.
A typical example of such a conventional marine jet drive is seen in U.S. Pat. No. 3,935,833, which shows a pump which may be driven vertically or horizontally and is positioned near the bottom and transom of a marine vessel. The conventional jet propulsion systems have certain general advantages that make them especially attractive under circumstances where a conventional ship""s propeller would be exposed to damage by contact with underwater objects. A jet drive has the further advantages that it does not produce appendage drag allowing more efficient operation and that it is safe for swimmers and animals that could be hurt by the rotating blades of an external propeller.
Despite these advantages, marine jet drives of the prior art have some problems and shortcomings, including as set forth below:
Among the problems with marine jet drives, as often with vessels having conventional propulsion means, are that the exhaust produces significant noxious odor, noise and heat signature behind and near the vessel, adversely affecting personnel on and near the vessel. In certain vessels with conventional propulsion means, exhaust can be released under water, which in theory can mitigate the problems to some extent. This in some cases can also be done with vessels having marine jet drives; however, as with conventional vessels, significant problems can remain.
Indeed, in marine jet drives, underwater exhausting is particularly problematic, because any exhaust gases in the water which is pumped into the jet drive unit from beneath the vessel will drastically interfere with operation of the jet drivexe2x80x94a very serious problem. Thus, the problems of noxious odors, noise and heat behind and near the vessel are particularly difficult to solve in vessels having marine jet drives.
In the past there have been some efforts to in some manner use the jet stream in connection with exhaust. One example is U.S. Pat. No. 3,943,876, which shows engine exhaust in combination with the jet stream; however, the exhaust is peripheral to the jet stream and is added behind the jet nozzle. The system of such patent does not significantly enhance efficiency or remove exhaust fumes and heat with the jet stream, nor does it serve to adequately suppress exhaust noise. U.S. Pat. No. 4,552,537 uses exhaust gases and engine-generated heat to decrease behind-the-jet nozzle frictional losses between a submerged jet stream and surrounding water in order to render the jet stream more effective.
In prior art marine jet drives, however, exhaust gases are not discharged with the jet stream. However, even if such an idea had been considered, difficult and highly significant problems would arise relating to a seeming inability to discharge the engine exhaust gas with the jet stream. The problem would be the matter of just how one would reasonably get the exhaust into the jet stream at the appropriate location.
In summary, substantial problems and shortcomings exist with respect to dealing with the engine exhaust of marine jet drives.
It is accordingly a primary object of the present invention to provide a marine jet drive propulsion system that overcomes problems and shortcomings of the prior art, including those set forth above.
Another object of this invention is to provide a marine jet drive propulsion system that overcomes disadvantages of the known jet drives.
Another object of this invention is to provide a marine jet drive which increases the comfort of people in the vessel by overcoming the problems of noxious odors, noise and heat behind and near the vessel.
Another object of this invention is to provide a marine jet drive which is quite and powerful in operation.
Another object of this invention is to provide a marine jet drive which avoids any release exhaust near the vessel.
Still another object of the invention is to provide a marine jet drive which successfully merges the engine exhaust stream into the jet stream of the jet drive at an appropriate location.
Yet another object of this invention is to provide a marine jet drive with improved engine performance.
These and other objects of the invention will be apparent from the following descriptions and from the drawings.
This invention is an improved marine jet drive which overcomes various problems and shortcomings of the prior art, including those referred to above. The invention is a marine jet drive system which places the engine exhaust internal to the jet stream of water. This serves to improve engine efficiency because of suction created by the jet stream, and greatly improves the comfort of people on the vessel by releasing the exhaust and its attendant noxious odors, noise and heat to the atmosphere well behind the vessel. The invention also involves particular structures which serve to allow engine exhaust to exit through the jet drive water stream.
Marine jet drives are, of course, powered by engines having exhaust lines. Each marine jet drive has an impeller and an impeller housing, a diffusor having a diffusor housing and stator vanes, a nozzle having a rearward end, and a water intake duct in front of the impeller housing. The improvement of this invention involves an inner housing which (a) is disposed inside the diffusor housing, (b) forms an inner exhaust chamber, (c) has an exhaust discharge tube portion that extends rearwardly into the nozzle and terminates in a rearward opening, and (d) is attached to the diffusor housing by the stator vanes. The exhaust line extends to the diffusor housing, and at least one of the stator vanes is hollow and open at its opposite ends to allow exhaust to flow from the exhaust line to the inner exhaust chamber, such that the exhaust exits through the exhaust discharge tube portion into the jet water flow.
Preferred embodiments include a plenum on the outside of the diffusor housing, such plenum feeding exhaust to a plurality of hollow stator vanes.
The preferred embodiments also preferably include a valve on the plenum which serves to vent the plenum when pressure in the plenum is greater than ambient pressure. Such valve remains closed when pressure in the plenum is not greater than ambient pressure. Operation of this valve allows continued outflow of exhaust during other than forward jet drive operation.
It is highly preferred that the exhaust discharge tube portion be removably attached to the remainder of the inner housing. This allows easy replacement.
More broadly defined, this invention involves an exhaust discharge outlet disposed inside a marine jet drive nozzle, the discharge outlet being in fluid communication with the engine exhaust line. The fluid communication preferably is through at least one of the stator vanes which are part of the diffusor.
This invention is also a method for improving performance of an engine which drives a marine jet drive, the jet drive including, of course, a nozzle for water outflow. The inventive method involves producing suction to facilitate exhaust flow from the engine by discharging exhaust within the water outflow at the nozzle. The enhanced exhaust outflow serves to improve engine performance.
In the method of this invention, exhaust discharge is preferably from an exhaust discharge tube which is surrounded by water outflow from the jet drive nozzle. The exhaust discharge most preferably occurs at a position substantially flush with the position of water discharge, in order to obtain a maximum suction effect. The exhaust discharge tube and the jet drive nozzle preferably have discharge ends which are substantially flush with one another.